Removal of cement from well casing



Sept. 16, 1958 H. M. KRAUSE, JR

REMOVAL OF' CEMENT FROM WELL CASING Filed Aug. 12

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ATTORNEY.

REMVAL F CEMENT FROM 'WELL CASING Henry M. Krause, Jr., Houston, Tex.,assignor, by mesne assignments, to Jersey Production Research CompanyApplication August 12, 1954i, Serial No. 449,294

3 Ciaims. (Cl. 1156-22) The present invention is directed to the removalof cement from well casing. More particularly, it is directed to methodand apparatus for removing at least a portion of a cement plug from awell casing. In its more specific aspects, the invention is directed tomethod and apparatus for working over wells having a casing arrangedtherein with a tubing arranged permanently in place with its lower endat a level above the working level in the casing.

The present invention may be briefly described as a method for removinga cement plug and the like from a. well casing having a tubingpermanently arranged therein with the lower open end of the tubing at alevel substantially above the level from which cement is to be removed.The method involves forcing a stream of an acid solution down the tubingand jetting the stream directly against the upper face of the cementplug to disintegrate the plug. During the time the stream of acid isjetted against the plug, the stream of acid solution follows the upperface yof the plug ,as it is being disintegrated. The acid solutioncontaining dissolved and/or disintegrated cement ows up the an nulusbetween the casing and the tubing. Thereafter the acid solution may bereturned to the tubing and again forced downwardly against the plug withthe stream of acid solution maintained in direct contact with the pluguntil at least a portion of the plug has 'been disintegrated and removedfrom the casing.

In practicing the present invention, it is contemplated that the acidsolution may be circulated up the casing between the casing and thetubing and again down the tubing against the upper face of the plug.Likewise, it is contemplated that, where a large amount of acid is notavailable or is not used, the acid solution may be forced up into theannulus and then forced back from the annulus into the tubing for re-usein jetting against the cement plug.

The present invention also contemplates apparatus for removing anddisintegrating a cement plug and the like in well casing in which atubing is arranged permanently in the casing with the lower end of thetubing at a level substantially above the working level or the levelwhere the cement plug is located. This apparatus comprises an elongatedtubular member adapted to be lowered through the tubing. Means areprovided for supporting the tubular member in the tubing and the tubularmember is provided with at least one telescopic member which is slidablycarried by the tubular member for lengthening the effective length ofthe tubular member when. the telescopic member is in a first positionand shortening the effective length of the tubular member when thetelescopic member is in a second position. The lower end of thetelescopic member may be suitably weighted such as by providing severaljoints of pipe below the point of telescoping for providing weight toand lengthening the member. At least one nozzle is arranged on or adjacent the free end of the telescopic member and the free end of thetelescopic member below the nozzles may be provided with a nozzle spacermember. The spacer member and the nozzle cooperate to allow the cementplug to be disintegrated by virtue .of acid being jetted through thenozzle. The spacer member maintains the nozzle a predetermined distancefrom the cement to achieve improved jetting effect of the acid.

The present invention is of considerable advantage and utility in theso-called permanent well completion A technique in which a tubing isarranged in a well casing with its lower open end located at a levelsubstantially above a working level or a point where a cement plug isarranged or preferably above an uppermost of a series or plurality ofhydrocarbon productive intervals, sand, strata, or formations. In thepermanent well completion operation, the tubing remains Xed in position,as originally located and all subsequent workover, recompletion andservice operations are conducted through the tubing by means of wireline tools and the like. Whenever a cement plug is left in the well andis too extensive or extends to too high a location, the presentinvention provides apparatus and method for removing same.

This invention involves jetting a stream of a mineral acid solution,such as commercial hydrochloric, nitric or sulfuric acid, hydroiluoricacid, or mixtures thereof against the face of the cement plug todisintegrate and/ or dissolve the same. lt is contemplated that the acid`or acids may be of any suitable concentration and may contain a.corrosion inhibiting agent, such as any of the well known mineral acidinhibitors; for example, soluble arsenic compounds, acid extracts ofpetroleum phenols, and many others too numerous to mention here.

ln the present invention, the stream of acid is jetted directly againstthe cement plug and is maintained against and follows the cement plug asthe level of the plug is diminished by disintegration or dissolution.

The present invention will be further illustrated by reference to thedrawing in which Fig. l shows the method and apparatus of the presentinvention for removing a plug from a well casing;

Fig. 2 illustrates the flow of acid solution back into the tubing; and

Fig. 3 shows the perforation of well casing after removal of the plug.

Referring now to the drawing and particulariy to Fig. l, numeral ildesignates a well bore which has been drilled from the earths surface,not shown, to penetrate a hydrocarbon productive interval A separated byan unproductive interval B from a second hydrocarbon interval C Arrangedin the well bore l1 is a casing 12 which is cemented in place with aprimary cement sheath 13. Suspended from the wellhead, not shown, at theearths surface, is a tubing 14 which is arranged with its lower end l5arranged at a level above thehydrocarbon productive interval A which maybe the uppermost of a plurality of hydrocarbon productive intervals.Arranged in the tubing i4 and projecting from the lower open end l5 is atubular member lo which is supported by a hanger assembly i8 at a pointadjacent the `lower end l5 of the tubing M in a landing nipple t7, suchas described in the Composite `Catalogue of Oil Field and Pipe LineEquipment, 19th edition, 1952-3, vol. 2, page 4052, Fig. 14. It is to beunderstood, however, that other supporting and/or securing means maysuitably be used for securing the upper end of the tubular member lo inthe tubing i4. The upper end of *he tubular member lo is 'also providedwith a suitable packing, generally indicated as 19, which may include asealing means, such as chevron packing and the like.

rlhe tubular member lo is also provided with a fishing neck, such as 2u,which engages with a shing tool ou Patented Sept. 16, 1958 the end of awire line for lowering same and retrieving the tubular member 16 fromthe tubing 1d.

Carried within the lower end 21 of the tubular member 15, which is ofincreased dimensions, is a slidable telescopic member 22 which isarranged to increase and decrease the effective length of the tubularmember 16 within the limits shown in Figs. l and 2. The telescopicmember 22 is provided 4with an external shoulder 23 which cooperateswith an internal shoulder 2d of the member 16 to retain the telescopicmember 22 within Ithe .member 16. The lower or free end of the member 22is provided with a plurality of nozzles 255 for Jietting a stream of aliquid, such as acid, against the cement plug 26, as will be describedfurther. Adjacent the nozzles on the free end of the member 22 is anozzle spacer member 27, which is used to correctly space the nozzlesabove the cement plug.

It is to be noted that the tubular member 16 and the telescopic member22 cooperate with the tubing 14 to define a continuous passagewayleading to the earths surface.

In the practice of the present invention, the perforations in the casing12 in the hydrocarbon productive interval C have `been formed and it isdesired to seal same oif due to waterland/ or gas invasion and the like.Under these conditions, a body or plug of cement 26 is arranged in thewell casing to seal the perforations 3ft and form the plug 26 therein.Under some conditions the height of the plug 26 is not controlledcarefully and it may extend up into and through the hydrocarbonproductive interval A from which it is desired to obtain production'. lninstances in accordance With the prior art, it would be necessary tomanipulate and raise the tubing string 14 and attach a bit thereto todrill out the plug 26. However, in accordance with the present inventionthe tubular member 16 is lowered on `a wire line and landed in thelanding nipple 17. This tubular member is provided with a telescopicmember 22 with the nozzle spacer member 27 resting on the upper face ofthe plug 26, A stream of an acid solution is then forced or pumped downthe tubing 14 and caused to issue through the nozzles 25' against theplug 26 dissolving and/ or disintegrating same, the llow being asindicated by the arrows with the `acid flowing down the tubing 14, thetubular member 16, and telescopic member 22 and up the annulus 40between the tubing 14 and the casing 12 and reclrculated bacl: againdown tubing 14. lt may be desirable to lilter or screen the acidsolution before it is again circulated down the tubing. Since it may notbe desirable to circulate a sufficient amount of acid or to pump acidcontinuously to form a continuous stream down the tubing and up theannulus to the earths surface, it is also contemplated with the presentinvention that the acid in the annulus after it has dissolved out atleast a portion of the plug 26, as shown in Fig. 2, may 4be forced 'nachdown the annulus 4b, through the nozzles 25, and up the telescopicmember 22 through member 21 and to the tubular 4member 16 and the tubing14. Thereafter uid pressure is imposed on the wellhead at the earthssurface, not shown, and the acid caused to be jetted again against theupper face of the partially removed plug 26.

After the plug 26 has 'been cut off or diminished to a point, as shownin Figs. 2 and 3, the tubular extension member 16 and the telescopicmember 22 maybe pulled from the landing nipple 17 and the tubing 14 bymeans of a wire line, leaving a full open tubing 14 for lowering ofother equipment through the lower open end 1S, In accordance with `thisinvention, a perforator, such as a gun perforator 42, is lowered on thewire line 41 from the wellhead until it has reached a level in thecasing adjacent the interval A above the diminished plug 26. Thisperforator may be a gun perforator of the bullet or shaped `charge typeor may be a mechanical perforator. The gun perforator may be lowered ona wire line or a conductor cable, both of which are generally indicated.cable 41 or tired from a power pack arranged in the perforator 42 asmay be desired. In any event, perforations, such as 44, are formed inthe casing 12 and the cement sheath 13 to penetrate the stratum orinterval A and allow production to be had therefrom into the tubing 14after withdrawal of the perforator 42.

It will be seen that the practice of the present invention allows theKremoval of cement plugs or lowering the level of the cement plug in aWell casing as desired without resorting to manipulation of the tubingstring which involves heavy duty lifting equipment and without resortingto rotary drilling operations.

As an example of the practice of the present invention, approximatelyfeet of a cement plug in a 5% inch casing was removed by jettingapproximately 3,000 gallons `of acid 'against the p-lug employingapparatus as illustrated in Figs. f1 and 2 with the acid streamimpinging directly on the upper face of the plug and following the plugsupper face downward as the plug was removed from the casing. Thisoperation was completed within 83 working lhours of which only 9% hourswere `actual jetting time.

`Cement removal is dependent on many factors such `as the degree ofhardness of the cement, the amount of cement to be removed, the amountof acid used per batch and the number of telescopic joints employed.Therefore, the invention is not to 'be restricted by any specificexamples which are given by way of illustration and not by way oflimitation.

While the invention has been described `and illustrated employing atelescopic means, such as 22, provided with nozzles 25 and nozzle spacer27, it is contemplated that the operation may be conducted with an openend member, such as 22, without using nozzles 25 or nozzle spacer 27although it is desired and preferred to Iuse nozzles, such as 25 and aspacer member such las 27 in the practice of the present invention inorder to afford a higher velocity of jetting action. A speciiic featureof the present device is that the nozzle 'spacer 27, during the cement4disintegrating operation, is constantly abutting the upper face of the'cement plug thereby automatically keeping the jetting action in a fixedrelationship to the top of the plug.

The practice of the present invention serves to remove lor `cut a cementplug by the action of the acid impinging on the plug at high velocity.This allows the cement plug to be removed at a satisfactory rate. Forexample, cement plugs may be removed from well casing at a rate in therange from about l5 to about 5 feet per vhour for casing havingdiameters in the range from about 5% inches ioutside diameter to about/8 inches outside diameter.

-It Will be seen that the practice lof the present invention is quiteadvantageous since workover rigs are no-t required and it is unnecessaryto pull tubing and return the tubing with the bit for drilling outcement.

The nature and objects of the .present invention having been completelydescribed and illustrated, what l wish to claim as new and useful and tosecure by Letters Patent is:

1. A method for removing a cement plug and the like from a Well casinghaving a tubing permanently arranged therein with the lower open end ofthe tubing at a level substantially above the level from which cement isto be removed which comprises forcing a stream of acid solution down thetubing to cause a jetting action directly against the upper face of saidcement plug to disintegrate at least a portion of said plug, maintainingthe maximum force of said jetting action of acid solution in directcontact with the upper face of said cement plug as it is disintegrated,and circulating said acid solution including the disintegrated cement upthe annulus between the casing and tubing, filtering said solution andagain forcing said.;

solution down the tubing directly against the upper face of the pluguntil at least a portion of said plug has been disintegrated and removedfrom the casing.

2. A method for removing a cement plug and the like from a well casinghaving a tubing permanently arranged therein with the lower open end ofthe tubing at a level substantially above the level from which cement isto be removed which comprises forcing a stream of acid solution down thetubing to cause a jetting action directly against the upper face ofcement plug to disintegrate at least a portion of said plug, maintainingthe jetting action of said stream of acid solution in a fixed spacedrelation with the upper face of said cement plug as it isdistintegrated, and circulating said acid solution up the annulusbetween lthe casing and tubing, returning the acid solution from theannulus to the tubing, and then again forcing the acid solution returnedto the tubing down the tubing and directly against the upper face of theplug until at least a portion of said plug has been disintegrated andthen circulating said solution and said disintegrated cement from thewell.

3. Apparatus for removing and dsintegrating a cement plug and the likefrom a well casing having a tubing arranged therein with the lower openend of the tubing at a level substantially above the level of the cementplug 'which comprises in combination an elongated tubular member adaptedto be lowered through the tubing, means for releasably latching saidtubular member in the tubing, packing means between said tubular memberand said tubing, at least one substantially rigid telescopic memberslidably arranged in said tubular member for lengthening the effectivelength of said tubular member when in a rst position and shortening theeffective lengthof said tubular member when in a second position, meansfor maintaining said telescopic member in said tubular member, at leastone nozzle positioned adjacent the free end of said telescopic memberfor directing a stream of acid solution' directly against said cementplug as said telescopic member moves from the second to the lirstposition and a nozzle spacer member positioned on the free end of saidtelescopic member adjacent said nozzle for maintaining a cons-tantspacing between s-aid nozzle and said cement plug.

References Cited in the le of this patent UNITED STATES PATENTS1,676,785 Lewis July 10, 1928 2,193,807 Dietrich Mar. 19, 1940 2,219,022Salmkov Oct. 22, 1940 2,271,005 Grebe Jan. 27, 1942 2,436,198 Cardwellet al Feb. 17, 1948 2,543,814 Thompson et al. Mar. 6, 1951 2,782,860Tausch et al. Feb. 26, 1957

2. A METHOD FOR REMOVING A CEMENT PLUG AND THE LIKE FORM A WELL CASINGHAVING A TUBING PERMANENTLY ARRANGED THEREIN WITH THE LOWER OPEN END OFTHE TUBING AT A LEVEL SUBSTANTIALLY ABOVE THE LEVEL FROM WHICH CEMENT ISTO BE REMOVED WHICH COMPRISES FORCING A STREAM OF ACID SOLUTION DOWN THETUBING TO CAUSE A JETTING ACTION DIRECTLY AGAINST THE UPPER FACE OFCEMENT PLUG TO DISINTERGRATE AT LEAST A PORTION OF SAID PLUG,MAINTAINING THE JETTING ACTION OF SAID STREAM OF ACID SOLUTION IN AFIXED SPACED RELATION WITH THE UPPER FACE OF SAID CEMENT PLUG AS IT ISDISTINTEGRATED, AND CIRCULATING SAID ACID SOLUTION UP THE ANNULUSBETWEEN THE CASING AND TUBING, RETURNING THE ACID SOLUTION FROM THEANNULUS TO THE TUBING, AND THEN AGAIN FORCING THE ACID SOLUTION RETURNEDTO THE TUBING DOWN THE TUBING AND DIRECTLY AGAINST THE UPPER FACE OF THEPLUG UNTIL AT LEAST A PORTION OF SAID PLUG HAS BEEN DISINTEGRATED ANDTHEN CIRCULATING SAID SOLUTION AND SAID DISINTEGRATED CEMENT FROM THEWELL.